1. Field of the Invention
The present invention relates to a high-frequency module used in, for example, a front end portion of a mobile phone.
2. Description of the Related Art
High-frequency modules that support multiple frequency bands use a single antenna for multiple communication systems using different frequency bands (for example, see Japanese Unexamined Patent Application Publication No. 2001-292073).
The high-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2001-292073 includes a diplexer connected to the antenna. A high-frequency signal circuit is isolated from a low-frequency signal circuit by the diplexer. The high-frequency signal circuit and the low-frequency signal circuit each include a switch circuit. The switch circuit includes a diode connected in series to a signal path for transmission signals and a diode connected in shunt to a signal path for reception signals. Switching off the diode provided in the switch circuit breaks the connection between the antenna and the signal path for transmission signals and makes the connection between the antenna and the signal path for reception signals. Switching on the diode makes the connection between the antenna and the signal path for transmission signals and breaks the connection between the antenna and the signal path for reception signals.
In general, when either of the high-frequency signal circuit and the low-frequency signal circuit is used in a typical high-frequency module, the transmission state or the reception state of the circuit that is used is switched by switching on or off the diode. The isolation between the low-frequency signal circuit and the high-frequency signal circuit is ensured by the diplexer provided therebetween. All of the diodes are switched off in the circuit that is not used.
If sufficient isolation is not ensured by the diplexer, there is a problem in that a transmission signal leaks from the circuit that is being used to the circuit that is not being used. Specifically, harmonic distortion can be caused in the diode in the circuit that is not being used, particularly, in the diode provided in the signal path for transmission signals to degrade the harmonic characteristics of the high-frequency module.